Study On The Miniaturized-Element Frequency Selective Surfaces

Frequency Selective Surface, which has been widely used in stealth radome, is aone-dimensional or two-dimensional periodic structure with band-pass or band-stopproperties. Miniaturized frequency selective surface (MEFSS) whose unit cell size ismuch smaller than its working wavelength is a new direction for FSS development.Compared with traditional FSS, MEFSS has miniaturized elements and stableresonance properties. It can be applied under special circumstances, such as in thelimited space, at a small local area, or non-plane wave illumination. MEFSS is ofgreat potential to design a structure with multiband, wideband and tunable properties,etc.On the back ground of the impending requirement of terminal guidance radome,this dissertation has discussed the physical mechanism, design principles andmethods of MEFSS based on in-depth theoretical analysis, numerical simulationsand practical experiments. And the main contents are as follows:1. According to the theory of electron movement, the operation mechanism ofthe FSS is analyzed on the view of microcosm. And from a macroscopic perspective,the filter mechanism of the FSS is studied based on the theory of field and circuit,respectively. Based on theory of field, the transmission properties of FSS, mainlyabout propagating wave, evanescent wave and grating lobes, are studied by using theFloquet modes. The necessary condition of getting stable filtering characteristics has been deduced from FSS’s grating lobe graph. And the influences of the mode on thetransmission properties of FSS are analyzed. Based on the theory of circuitry, it isstudied about how to establish equivalent circuit model of FSS and analyze thefiltering mechanism. This part unveils that it is feasible to analyze the complex FSSstructure by the equivalent circuit model based on curve-fitting process. It will givesome references for the quick calculation of FSS transmission characteristics duringdesign and optimization stages.2. The MEFSS which is based on the mechanism of coupling the capacitivesurface and the inductive surface is studied. Moreover, three typical MEFSSstructures are used to design Ku-band MEFSS. From that, the design principles andideas of MEFSS that work at Ku-band are obtained. Then MEFSSs with a pass-bandat Ku-band, which are applied to a solid wall radome and A-sandwiched radome, aredesigned and analyzed.3. Based on the studies of the complementary and symmetric structures, awideband MEFSS is presented. It is composed of three metallic layers with skewedarrays (60°) of modified tripoles. This MEFSS has the properties of miniaturizedelements, wider bandwidth and maximally flat (Butterworth) response. The MEFSSswith a desired wide pass-band at least at X or Ku-band are designed, and theprinciples of operation, the influences of the parameters, the experimental values ofthe fabricated prototype are presented and discussed. It is useful for designingwideband FSSs with flat top and sharp cut-off.4. The coupling and resonance mechanism are exploited to design MEFSS. Thedesigned structure is composed of three metallic layers, and can obtain twopass-bands at Ku-band and millimeter-wave region. Using it to design stealthradome, a MEFSS on the solid wall radome or A-sandwich radome substrate isdesigned and fabricated. The proposed radome structure with FSS can achieve twostable pass-bands at Ku-/Ka-band. It is useful for designing multi-band and wideband spacing FSS.5. In order to further reduce the unit size of the FSS that especially worked at low frequency, the MEFSS loading lumped components are studied. Using thepassive lumped components—capacitances and inductances, the unit size of thedesigned MEFSS can reduce to λ0/28, and by optimization, this structure has aproperty of polarization separation at the same time. Using the active lumpedcomponents—PIN diodes, as long as the diode working frequency allows, thedesigned MEFSS is electronically switchable between reflective and transparentstates at S-band by switching PIN diodes to ON and OFF state, and always has apass-band at Ku-band. It is useful for designing electronically switchable stealthradome.In this dissertation, the study of MEFSS is mainly prepared for the special needsof stealth radome, such as wideband, dual-band with wide band spacing,electronically switchable at crucial frenquency, etc. It not only improves the designtheory of MEFSS, but also expands the approaches and applications of MEFSStechnology. And it provides some theoretical and experimental references for theapplication of MEFSS in stealth radomes.